Wireless communication transmitters that are used to carry high linear modulation formatted signals, such as Wireless LAN (WLAN) signals, are often required to transmit relatively high transmit power. At high transmitted power levels, however, the noise floor (also referred to as the Error Vector Magnitude or EVM) contribution from the power amplifier (PA) becomes high as well.
Manufacturers designing and building products such as communication devices, often design their products to operate in accordance with industry standards. Often, the transmitter is built to implement a wireless standard such as WLAN, GSM, Bluetooth, etc. In order to meet the EVM requirements of the standard, the power of the signal input to the power amplifier must be calibrated so that the EVM will meet the requirements imposed by the standard. Typically, the transmitter is calibrated during production line testing of the solution (comprising the chip or SoC and the external power amplifier) which is performed per device on the target PCB.
Prior art testing of communication devices requires the device to be connected to one or more pieces of external test equipment that perform a battery of tests to ensure compliance with the specifications. The test equipment used is typically bulky in size, costly and requires routine maintenance and calibration of its own.
A diagram illustrating an example prior art production line testing scenario is shown in FIG. 1. The test setup, generally referenced 10, comprises a phone printed circuit board (PCB) 12, power meter test equipment 14, EVM meter and spectrum plot test equipment 16 and a PC or other computing means 18 running the prior art calibration control process. The DUT 20 comprises the WLAN chip or integrated circuit (IC) 22 and external front end module (FEM) 24.
In operation, the prior art calibration and control process controls the DUT via the data/control lines 29. Measurements of the RF output 21 from the FEM are taken via the power meter 14 and the EVM meter/spectrum plot 16. The measurement results from the power meter and EVM meter are read by the calibration control process via data/control lines 28, 26, respectively.
Existing production line testing techniques requires one or more measurements of the TX output power and/or other signals using external test equipment and the storing of the results in non-volatile storage (NVS). The testing is performed on the cell phone production line whereby the test equipment communicates extensively with the cell phone SoC, PCB assemblies, etc. which consumes a considerable amount of time thus making this testing process very costly.
There is thus a need for a mechanism that is capable of calibrating the digital gain of the power amplifier that is required to maximize the EVM and spectral mask of the radio. The mechanism preferably does not require the use of expensive test equipment or require long expensive test time on the production line.